Fillers are probably the most widely used additive in thermoplastic resins. They are typically employed for economic reasons, i.e., to reduce the cost of relatively high priced resins, and/or to impart a particular property to a resin; e.g., increased modulus, flame retardancy, improved heat distortion, and the like. There is, however, a disadvantage in employing particulate fillers with thermoplastic polycarbonate resins. Many of the particulate fillers such as calcined clays, talc, earth metal salts, glass and the like contain reactive hydroxyl (--OH) groups which, when incorporated in a thermoplastic polycarbonate resin composition, tend to react with and thereby degrade the resin, especially when the resin composition is exposed to moisture.
Prior attempts to inactivate these free reactive groups include mixing the particulate fillers which such compounds as siloxanes, arylsiloxanes, silanols, and the like. While, these compounds readily coat such particulates, they are not effective in rendering the reactive groups inert since they are easily removed or become separated from the particulate fillers.
When employed with thermoplastic polycarbonate resins, particulate fillers detract from such physical properties of the resins as impact strength, thermal stability and the like while improving such properties as modulus. In the past fiberglass has been used in a similar manner in order to get a high modulus. However, fiberglass is more expensive than particulates and it likewise adversely affects such properties as impact strength.